Molybdenum occurs chiefly as molybdenite (MoS2) and is often present in small amounts in ores also containing copper.
Typically, such an ore contains about 0.5% to 1% Cu (as sulphide) and about 0.01 to 0.03% Mo, by weight, although these concentrations vary widely. The ore is usually treated in a concentrator to produce a bulk concentrate containing about 25%–40% Cu and about 0.3%–2% Mo. The bulk concentrate is then treated in a molybdenum separation plant to produce a Cu concentrate and a Mo concentrate containing about 50% Mo and about 0.1–10% Cu as copper sulphide. The % Cu in the Mo concentrate varies widely as the separation of Cu from Mo is sometimes difficult and expensive. If the % Cu in the Mo concentrate is above about 0.25% Cu, it may incur a penalty in the market, or be difficult to market at all when the market is over-supplied. Mo concentrates containing high Cu, above 0.75%, are sometimes referred to as dirty Mo concentrates.
The dirty Mo concentrate is sometimes subjected to a leach process with a concentrated or strong ferric chloride solution, typically about 50 to 100 g/L chloride to produce a solution containing Cu and a low copper Mo concentrate containing less than about 0.25% Cu, as required by the market, in order to avoid the payment of a penalty. The amount of the penalty increases as the amount of Cu in the Mo concentrate increases.
The ferric chloride leach, however, is a capital intensive process with high operating costs. Copper recovery from the leach solution is difficult because of the high chloride content so that the solution is often discarded or blended with a heap leaching operation, which however results in chloride contamination and reagent losses. As a result of the high cost, some mining operations do not use the leaching process. They simply endeavour to produce the best quality Mo concentrate possible under the circumstances, which concentrate is then marketed taking the penalty for having a Cu concentration which is above the required maximum value.
There is, however, a trade-off between the amount of Cu in the high copper Mo concentrate produced by the process and the amount of Mo recovery to the Mo concentrate. The smaller the amount of Cu present in the Mo concentrate, the poorer the Mo recovery from the concentrate. Thus, it is beneficial to have a copper presence in the high copper Mo concentrate but, as indicated above, the presence of copper is problematical when using conventional processes.
It is accordingly an object of the present invention to provide an alternative process for the recovery of Mo from the so-called dirty Mo concentrate referred to above.
It is also an object of the invention to remove impurities, such as Mo and As, from a copper containing solution during a copper recovery process.